Re: [RFH] Why do osx CI jobs so unreliable?

Re: [RFH] Why do osx CI jobs so unreliable?

[Michael Montalbo]

Patrick Steinhardt <ps@pks.im> writes:
> So I strongly suspect that it most be one of the t555* tests.
> [...]
> Maybe this is something that's specific to GitHub's environment...

I think you're right it's t5551/t5559. The runs Junio linked:

  osx-clang     cancelled  360min
  osx-gcc       cancelled  360min
  osx-reftable  success     35min
  osx-meson     success     61min

All four run the same t5551/t5559 under EXPENSIVE. The two that
finished differ in just two ways, which look like the levers:
osx-reftable generates the 100k-ref advertisement in ~24ms vs ~1.2s
for loose refs on macOS (so much less time mid-response), and
osx-meson runs tests at nproc while the prove jobs hardcode --jobs=10
on a 3-core runner (over recent master/next the prove jobs hang ~40%,
meson ~10%).

When it is wedged the whole chain sits at 0% CPU. upload-pack is
blocked in write() on the ls-refs advertisement, curl blocked in
select(). So it looks like an HTTP/2 flow-control stall on the
response side. The same stall resets itself after ~60-85s on my Linux
box and on a bare-metal Mac, but not on the GitHub runner; I haven't
pinned down why yet.

On the chance those two levers are the fix, a branch off master:

  https://github.com/mmontalbo/git/tree/mm/macos-ci-hang-fix

  - pack the refs in t5551's enormous-ref-negotiation test (doesn't
    change what it checks on the wire, just avoids re-reading 100k loose
    files to advertise them, like reftable already does)
  - use the core count for $JOBS on the GitHub macOS path, matching the
    GitLab branch in the same ci/lib.sh and what meson does

I ran the two macOS jobs under EXPENSIVE about eight times with these
and they all finished in ~30-44min instead of hanging. Happy to send
out a patch if it's helpful.

Re: [RFH] Why do osx CI jobs so unreliable?

[Jeff King]

On Sat, Jun 20, 2026 at 08:33:13AM -0700, Michael Montalbo wrote:

> Patrick Steinhardt <ps@pks.im> writes:
> > So I strongly suspect that it most be one of the t555* tests.
> > [...]
> > Maybe this is something that's specific to GitHub's environment...
> 
> I think you're right it's t5551/t5559. The runs Junio linked:
> 
>   osx-clang     cancelled  360min
>   osx-gcc       cancelled  360min
>   osx-reftable  success     35min
>   osx-meson     success     61min
> 
> All four run the same t5551/t5559 under EXPENSIVE. The two that
> finished differ in just two ways, which look like the levers:
> osx-reftable generates the 100k-ref advertisement in ~24ms vs ~1.2s
> for loose refs on macOS (so much less time mid-response), and
> osx-meson runs tests at nproc while the prove jobs hardcode --jobs=10
> on a 3-core runner (over recent master/next the prove jobs hang ~40%,
> meson ~10%).

If the problem is a racy deadlock, there is a reasonable chance that
some jobs may simply be lucky. Even if things like packing refs help, I
suspect the problem may still be lurking. Maybe I'm just a pessimist,
though. ;)

> When it is wedged the whole chain sits at 0% CPU. upload-pack is
> blocked in write() on the ls-refs advertisement, curl blocked in
> select(). So it looks like an HTTP/2 flow-control stall on the
> response side. The same stall resets itself after ~60-85s on my Linux
> box and on a bare-metal Mac, but not on the GitHub runner; I haven't
> pinned down why yet.

We had some HTTP/2 stalls/deadlocks in the past, and they were dependent
on libcurl and apache (actually h2_mod) versions. IIRC some of the
non-TLS code paths for HTTP/2 were not well tested, which led to
8f2146dbf1 (t5559: make SSL/TLS the default, 2023-02-23). Of course
after that commit those cleartext code paths should not be a problem, so
that is probably not exactly the issue now.

But it might be worth checking the versions you're running locally
versus what's in the GitHub runner.

-Peff

Re: [RFH] Why do osx CI jobs so unreliable?

[Patrick Steinhardt]

On Sun, Jun 21, 2026 at 05:34:07PM -0400, Jeff King wrote:
> On Sat, Jun 20, 2026 at 08:33:13AM -0700, Michael Montalbo wrote:
> 
> > Patrick Steinhardt <ps@pks.im> writes:
> > > So I strongly suspect that it most be one of the t555* tests.
> > > [...]
> > > Maybe this is something that's specific to GitHub's environment...
> > 
> > I think you're right it's t5551/t5559. The runs Junio linked:
> > 
> >   osx-clang     cancelled  360min
> >   osx-gcc       cancelled  360min
> >   osx-reftable  success     35min
> >   osx-meson     success     61min
> > 
> > All four run the same t5551/t5559 under EXPENSIVE. The two that
> > finished differ in just two ways, which look like the levers:
> > osx-reftable generates the 100k-ref advertisement in ~24ms vs ~1.2s
> > for loose refs on macOS (so much less time mid-response), and
> > osx-meson runs tests at nproc while the prove jobs hardcode --jobs=10
> > on a 3-core runner (over recent master/next the prove jobs hang ~40%,
> > meson ~10%).
> 
> If the problem is a racy deadlock, there is a reasonable chance that
> some jobs may simply be lucky. Even if things like packing refs help, I
> suspect the problem may still be lurking. Maybe I'm just a pessimist,
> though. ;)

I had the same thought.

> > When it is wedged the whole chain sits at 0% CPU. upload-pack is
> > blocked in write() on the ls-refs advertisement, curl blocked in
> > select(). So it looks like an HTTP/2 flow-control stall on the
> > response side. The same stall resets itself after ~60-85s on my Linux
> > box and on a bare-metal Mac, but not on the GitHub runner; I haven't
> > pinned down why yet.
> 
> We had some HTTP/2 stalls/deadlocks in the past, and they were dependent
> on libcurl and apache (actually h2_mod) versions. IIRC some of the
> non-TLS code paths for HTTP/2 were not well tested, which led to
> 8f2146dbf1 (t5559: make SSL/TLS the default, 2023-02-23). Of course
> after that commit those cleartext code paths should not be a problem, so
> that is probably not exactly the issue now.
> 
> But it might be worth checking the versions you're running locally
> versus what's in the GitHub runner.

I didn't observe any similar hangs in GitLab's CI systems, so I wonder
whether this is because of different versions of curl. And indeed we use
different versions:

  - On GitHub we use 8.6.0.

  - On GitLab we use 8.7.1.

Now this of course doesn't mean that updating the curl version is the
fix to this whole issue, as there's a ton of other factors that could
play a role in whether or not the test hangs. So while we could just
upgrade parts of the stack and cross our fingers, but that feels rather
unsatisfactory. Still, one place to start could be to update our build
images to macOS 15.

But the big question to me is whether the hang is because of a bug in
Git with how we drive curl, a bug in curl itself, or a bug in Apache.

Patrick

Re: [RFH] Why do osx CI jobs so unreliable?

[Patrick Steinhardt]

On Mon, Jun 22, 2026 at 06:42:24AM +0200, Patrick Steinhardt wrote:
> On Sun, Jun 21, 2026 at 05:34:07PM -0400, Jeff King wrote:
> > On Sat, Jun 20, 2026 at 08:33:13AM -0700, Michael Montalbo wrote:
[snip]
> > > When it is wedged the whole chain sits at 0% CPU. upload-pack is
> > > blocked in write() on the ls-refs advertisement, curl blocked in
> > > select(). So it looks like an HTTP/2 flow-control stall on the
> > > response side. The same stall resets itself after ~60-85s on my Linux
> > > box and on a bare-metal Mac, but not on the GitHub runner; I haven't
> > > pinned down why yet.
> > 
> > We had some HTTP/2 stalls/deadlocks in the past, and they were dependent
> > on libcurl and apache (actually h2_mod) versions. IIRC some of the
> > non-TLS code paths for HTTP/2 were not well tested, which led to
> > 8f2146dbf1 (t5559: make SSL/TLS the default, 2023-02-23). Of course
> > after that commit those cleartext code paths should not be a problem, so
> > that is probably not exactly the issue now.
> > 
> > But it might be worth checking the versions you're running locally
> > versus what's in the GitHub runner.
> 
> I didn't observe any similar hangs in GitLab's CI systems, so I wonder
> whether this is because of different versions of curl. And indeed we use
> different versions:
> 
>   - On GitHub we use 8.6.0.
> 
>   - On GitLab we use 8.7.1.
> 
> Now this of course doesn't mean that updating the curl version is the
> fix to this whole issue, as there's a ton of other factors that could
> play a role in whether or not the test hangs. So while we could just
> upgrade parts of the stack and cross our fingers, but that feels rather
> unsatisfactory. Still, one place to start could be to update our build
> images to macOS 15.
> 
> But the big question to me is whether the hang is because of a bug in
> Git with how we drive curl, a bug in curl itself, or a bug in Apache.

I noticed that a osx-clang job failed today in t5551 [1]. This time it
didn't hang, but produced an actual error:

    2026-06-22T09:25:45.1984230Z ++ git -C too-many-refs fetch -q --tags
    2026-06-22T09:25:45.1984420Z error: RPC failed; curl 18 transfer closed with outstanding read data remaining
    2026-06-22T09:25:45.1984520Z fatal: expected flush after ref listing
    2026-06-22T09:25:45.1984610Z error: last command exited with $?=128
    2026-06-22T09:25:45.1984660Z ++ rm -f tags
    2026-06-22T09:25:45.1984710Z ++ :
    2026-06-22T09:25:45.1984830Z not ok 35 - http can handle enormous ref negotiation

There was a second test failing similarly.

Patrick

[1]: https://github.com/git/git/actions/runs/27940620478/job/82672854726

Re: [RFH] Why do osx CI jobs so unreliable?

[Patrick Steinhardt]

On Mon, Jun 22, 2026 at 11:48:01AM +0200, Patrick Steinhardt wrote:
> On Mon, Jun 22, 2026 at 06:42:24AM +0200, Patrick Steinhardt wrote:
> > On Sun, Jun 21, 2026 at 05:34:07PM -0400, Jeff King wrote:
> > > On Sat, Jun 20, 2026 at 08:33:13AM -0700, Michael Montalbo wrote:
> [snip]
> > > > When it is wedged the whole chain sits at 0% CPU. upload-pack is
> > > > blocked in write() on the ls-refs advertisement, curl blocked in
> > > > select(). So it looks like an HTTP/2 flow-control stall on the
> > > > response side. The same stall resets itself after ~60-85s on my Linux
> > > > box and on a bare-metal Mac, but not on the GitHub runner; I haven't
> > > > pinned down why yet.
> > > 
> > > We had some HTTP/2 stalls/deadlocks in the past, and they were dependent
> > > on libcurl and apache (actually h2_mod) versions. IIRC some of the
> > > non-TLS code paths for HTTP/2 were not well tested, which led to
> > > 8f2146dbf1 (t5559: make SSL/TLS the default, 2023-02-23). Of course
> > > after that commit those cleartext code paths should not be a problem, so
> > > that is probably not exactly the issue now.
> > > 
> > > But it might be worth checking the versions you're running locally
> > > versus what's in the GitHub runner.
> > 
> > I didn't observe any similar hangs in GitLab's CI systems, so I wonder
> > whether this is because of different versions of curl. And indeed we use
> > different versions:
> > 
> >   - On GitHub we use 8.6.0.
> > 
> >   - On GitLab we use 8.7.1.
> > 
> > Now this of course doesn't mean that updating the curl version is the
> > fix to this whole issue, as there's a ton of other factors that could
> > play a role in whether or not the test hangs. So while we could just
> > upgrade parts of the stack and cross our fingers, but that feels rather
> > unsatisfactory. Still, one place to start could be to update our build
> > images to macOS 15.
> > 
> > But the big question to me is whether the hang is because of a bug in
> > Git with how we drive curl, a bug in curl itself, or a bug in Apache.
> 
> I noticed that a osx-clang job failed today in t5551 [1]. This time it
> didn't hang, but produced an actual error:
> 
>     2026-06-22T09:25:45.1984230Z ++ git -C too-many-refs fetch -q --tags
>     2026-06-22T09:25:45.1984420Z error: RPC failed; curl 18 transfer closed with outstanding read data remaining
>     2026-06-22T09:25:45.1984520Z fatal: expected flush after ref listing
>     2026-06-22T09:25:45.1984610Z error: last command exited with $?=128
>     2026-06-22T09:25:45.1984660Z ++ rm -f tags
>     2026-06-22T09:25:45.1984710Z ++ :
>     2026-06-22T09:25:45.1984830Z not ok 35 - http can handle enormous ref negotiation
> 
> There was a second test failing similarly.

Oh, and Linux is also failing in the same test suite [1], even though
the job logs are truncated, so it's hard to say whether it's the same
failure or not.

There certainly seems to be a deeper issue here. We could of course just
disable the test again, but by now I do wonder whether this would paper
over an actual bug.

Patrick

[1]: https://github.com/git/git/actions/runs/27940620478/job/82672854864

Re: [RFH] Why do osx CI jobs so unreliable?

[Patrick Steinhardt]

On Mon, Jun 22, 2026 at 11:55:31AM +0200, Patrick Steinhardt wrote:
> On Mon, Jun 22, 2026 at 11:48:01AM +0200, Patrick Steinhardt wrote:
> > On Mon, Jun 22, 2026 at 06:42:24AM +0200, Patrick Steinhardt wrote:
> > > On Sun, Jun 21, 2026 at 05:34:07PM -0400, Jeff King wrote:
> > > > On Sat, Jun 20, 2026 at 08:33:13AM -0700, Michael Montalbo wrote:
> > [snip]
> > > > > When it is wedged the whole chain sits at 0% CPU. upload-pack is
> > > > > blocked in write() on the ls-refs advertisement, curl blocked in
> > > > > select(). So it looks like an HTTP/2 flow-control stall on the
> > > > > response side. The same stall resets itself after ~60-85s on my Linux
> > > > > box and on a bare-metal Mac, but not on the GitHub runner; I haven't
> > > > > pinned down why yet.
> > > > 
> > > > We had some HTTP/2 stalls/deadlocks in the past, and they were dependent
> > > > on libcurl and apache (actually h2_mod) versions. IIRC some of the
> > > > non-TLS code paths for HTTP/2 were not well tested, which led to
> > > > 8f2146dbf1 (t5559: make SSL/TLS the default, 2023-02-23). Of course
> > > > after that commit those cleartext code paths should not be a problem, so
> > > > that is probably not exactly the issue now.
> > > > 
> > > > But it might be worth checking the versions you're running locally
> > > > versus what's in the GitHub runner.
> > > 
> > > I didn't observe any similar hangs in GitLab's CI systems, so I wonder
> > > whether this is because of different versions of curl. And indeed we use
> > > different versions:
> > > 
> > >   - On GitHub we use 8.6.0.
> > > 
> > >   - On GitLab we use 8.7.1.
> > > 
> > > Now this of course doesn't mean that updating the curl version is the
> > > fix to this whole issue, as there's a ton of other factors that could
> > > play a role in whether or not the test hangs. So while we could just
> > > upgrade parts of the stack and cross our fingers, but that feels rather
> > > unsatisfactory. Still, one place to start could be to update our build
> > > images to macOS 15.
> > > 
> > > But the big question to me is whether the hang is because of a bug in
> > > Git with how we drive curl, a bug in curl itself, or a bug in Apache.
> > 
> > I noticed that a osx-clang job failed today in t5551 [1]. This time it
> > didn't hang, but produced an actual error:
> > 
> >     2026-06-22T09:25:45.1984230Z ++ git -C too-many-refs fetch -q --tags
> >     2026-06-22T09:25:45.1984420Z error: RPC failed; curl 18 transfer closed with outstanding read data remaining
> >     2026-06-22T09:25:45.1984520Z fatal: expected flush after ref listing
> >     2026-06-22T09:25:45.1984610Z error: last command exited with $?=128
> >     2026-06-22T09:25:45.1984660Z ++ rm -f tags
> >     2026-06-22T09:25:45.1984710Z ++ :
> >     2026-06-22T09:25:45.1984830Z not ok 35 - http can handle enormous ref negotiation
> > 
> > There was a second test failing similarly.
> 
> Oh, and Linux is also failing in the same test suite [1], even though
> the job logs are truncated, so it's hard to say whether it's the same
> failure or not.
> 
> There certainly seems to be a deeper issue here. We could of course just
> disable the test again, but by now I do wonder whether this would paper
> over an actual bug.
> 
> Patrick
> 
> [1]: https://github.com/git/git/actions/runs/27940620478/job/82672854864

Sorry for the repeated spam.

I think the issue is rather simple: we're hitting timeouts in Apache. If
you apply the following diff:

diff --git a/t/lib-httpd/apache.conf b/t/lib-httpd/apache.conf
index 40a690b0bb..4054fe008f 100644
--- a/t/lib-httpd/apache.conf
+++ b/t/lib-httpd/apache.conf
@@ -302,3 +302,5 @@ RewriteRule ^/half-auth-complete/ - [E=AUTHREQUIRED:yes]
 		SVNPath "${LIB_HTTPD_SVNPATH}"
 	</Location>
 </IfDefine>
+
+Timeout 1

Then you'll see the same errors locally:

    $ GIT_TEST_LONG=Yes meson test t5551-http-fetch-smart --test-args=-ix -i
    Failed to clone 'sub'. Retry scheduled
    Cloning into '/home/pks/Development/git/build/test-output/trash directory.t5551-http-fetch-smart/sub'...
    error: RPC failed; curl 18 transfer closed with outstanding read data remaining
    fatal: early EOF
    fatal: fetch-pack: invalid index-pack output
    fatal: clone of 'http://127.0.0.1:5551/smart_headers/repo.git' into submodule path '/home/pks/Development/git/build/test-output/trash directory.t5551-http-fetch-smart/sub' failed
    Failed to clone 'sub' a second time, aborting
    error: last command exited with $?=1
    not ok 36 - custom http headers
    #	
    #		test_must_fail git -c http.extraheader="x-magic-two: cadabra" \
    #			fetch "$HTTPD_URL/smart_headers/repo.git" &&
    #		git -c http.extraheader="x-magic-one: abra" \
    #		    -c http.extraheader="x-magic-two: cadabra" \
    #		    fetch "$HTTPD_URL/smart_headers/repo.git" &&
    #		git update-index --add --cacheinfo 160000,$(git rev-parse HEAD),sub &&
    #		git config -f .gitmodules submodule.sub.path sub &&
    #		git config -f .gitmodules submodule.sub.url \
    #			"$HTTPD_URL/smart_headers/repo.git" &&
    #		git submodule init sub &&
    #		test_must_fail git submodule update sub &&
    #		git -c http.extraheader="x-magic-one: abra" \
    #		    -c http.extraheader="x-magic-two: cadabra" \
    #			submodule update sub
    #	
    1..36

And Apache also logs this as a timeout:

    [Mon Jun 22 10:26:52.115717 2026] [cgi:warn] [pid 3686957:tid 3686957] [client 127.0.0.1:55114] AH01220: Timeout waiting for output from CGI script /home/pks/Development/git/build/git-http-backend
    [Mon Jun 22 10:26:52.115748 2026] [core:error] [pid 3686957:tid 3686957] (70007)The timeout specified has expired: [client 127.0.0.1:55114] AH00574: ap_content_length_filter: apr_bucket_read() failed
    [Mon Jun 22 10:27:01.567533 2026] [cgi:warn] [pid 3686958:tid 3686958] [client 127.0.0.1:54384] AH01220: Timeout waiting for output from CGI script /home/pks/Development/git/build/git-http-backend
    [Mon Jun 22 10:27:01.567559 2026] [core:error] [pid 3686958:tid 3686958] (70007)The timeout specified has expired: [client 127.0.0.1:54384] AH00574: ap_content_length_filter: apr_bucket_read() failed

This is because our keepalive mechanisms aren't helping:

  - The TCP-level keepalives don't help with Apache.

  - The application-level sideband keepalives don't apply to the
    "ls-refs" endpoint.

Whether that's the same issue like we see in macOS sometimes is a
different question.

Patrick

Re: [RFH] Why do osx CI jobs so unreliable?

[Michael Montalbo]

Patrick Steinhardt <ps@pks.im> writes:
> I think the issue is rather simple: we're hitting timeouts in Apache.
> [...]
> This is because our keepalive mechanisms aren't helping [...]
> Whether that's the same issue like we see in macOS sometimes is a
> different question.

I think that is the trigger for issues we've been seeing. I spent
some time investigating the Apache side over the last week and maybe
found a mod_http2 bug, which I filed upstream with a potential fix:

  bug:  https://bz.apache.org/bugzilla/show_bug.cgi?id=70131
  fix:  https://github.com/mmontalbo/httpd/pull/2

To Patrick's earlier question of whether this is a Git, curl, or Apache
bug: as best I can tell it's Apache. I could reproduce it with no Git
involved at all (just Apache and a small CGI that goes quiet past the
Timeout), and across several curl versions (8.6.0, which is what the
GitHub runners use, up to 8.20.0), so I don't think bumping curl would
help. It also seems to wear two faces from the same trigger: over
HTTP/1.1 Apache closes the connection and curl bails with the
"transfer closed" error (which looks like what you hit with Timeout=1,
and the recent failures on both macOS and Linux), and over HTTP/2 it
does not reliably reset the stream, so the client just waits, which is
the six-hour macOS hang. I share the pessimism from earlier in the
thread, though: I think the real fix is upstream in Apache, and
anything we do on our side mostly just bounds the symptom in the
meantime.

Given there could be a potential reliability issue with an upstream
dependency like Apache, I was considering what mitigation strategies
might help:

  - Enforce some kind of lower bound speed limit and a client-side
    timeout so runs that wedge fail fast (and loudly) instead of
    hanging.

  - Potentially provide some affordance for retrying flaky tests
    that might fail due to upstream dependencies. Git already has
    some HTTP retry support (http.maxRetries and friends, added
    recently), but as far as I can tell it only triggers on HTTP 429
    rate limiting, so it would not catch a stall like this on its
    own. A test-level retry is not something I like that much, since
    it might encourage papering over flakiness that should be
    resolved, but it was a consideration vs requiring a fresh CI run
    to resolve the flake.

  - Make slow tests faster by optimizing the test itself and/or
    the test runner configuration (e.g., job number matching
    cores) so wedges become less likely.

For the first one, I think Git already provides some affordances. There
is a stall-based timeout that just ships disabled: as I understand it
http.lowSpeedLimit sets a bytes/sec floor and http.lowSpeedTime how long
a transfer can sit below it before curl gives up, so it would catch a
wedged connection without punishing one that is just slow. Enabling it
for the http tests might look something like:

    diff --git a/t/lib-httpd.sh b/t/lib-httpd.sh
    @@ GIT_TRACE=$GIT_TRACE; export GIT_TRACE
    +# Abort a transfer that makes essentially no progress for a while,
    +# so a wedged connection fails in seconds instead of hanging to the
    +# job cap. Tiny limit, generous window, so it only trips on a true
    +# stall; override either var, or set the limit to 0, to disable.
    +GIT_HTTP_LOW_SPEED_LIMIT=${GIT_HTTP_LOW_SPEED_LIMIT-1}
    +GIT_HTTP_LOW_SPEED_TIME=${GIT_HTTP_LOW_SPEED_TIME-60}
    +export GIT_HTTP_LOW_SPEED_LIMIT GIT_HTTP_LOW_SPEED_TIME

I went conservative on the values on purpose: a floor of 1 byte/sec
should only really fire on a true zero-progress stall, not on something
that is just crawling on a slow runner, and the 60s window is generous
for the same reason. When I tried it locally against a stall-proxy it
did turn an otherwise indefinite hang into a bounded abort (a tighter
limit/window brings that down to single-digit seconds). It probably does
not need to be suite-wide either; it could be scoped per-command with
git -c, which the http tests already lean on for this kind of thing
(t5551 passes http.postbuffer and http.extraheader that way), if a
narrower blast radius feels safer.

I only dug into the first option in any depth, since I wanted to
sanity-check the direction before writing patches. Does turning on a
stall timeout for the http tests seem reasonable? Are there other
strategies that we should implement?

Re: [RFH] Why do osx CI jobs so unreliable?

[Jeff King]

On Thu, Jun 25, 2026 at 08:27:35PM -0700, Michael Montalbo wrote:

> I think that is the trigger for issues we've been seeing. I spent
> some time investigating the Apache side over the last week and maybe
> found a mod_http2 bug, which I filed upstream with a potential fix:
> 
>   bug:  https://bz.apache.org/bugzilla/show_bug.cgi?id=70131
>   fix:  https://github.com/mmontalbo/httpd/pull/2

Thanks both of you for digging into this. I'm not familiar enough with
Apache's code to pass confident judgement, but your findings certainly
convinced me that this is just an apache bug.

> Given there could be a potential reliability issue with an upstream
> dependency like Apache, I was considering what mitigation strategies
> might help:
> [...]

Depending on how widespread the Apache bug is, another option might just
be: do nothing and wait for it to get fixed.

Trying to make the wedged state fail fast and loudly is mostly just
punting on the problem. We'd still see spurious failures. We've so far
resisted the urge to do any automatic flaky-test retries, preferring
instead to just try to root out the flakes. I'm a little hesitant to
start now, because I think our strategy has mostly been good so far, and
I've seen some horrible counter-examples where flakes and retries become
a routine drag on development (and I'm afraid that accommodating flakes
might make them more common).

>   - Make slow tests faster by optimizing the test itself and/or
>     the test runner configuration (e.g., job number matching
>     cores) so wedges become less likely.

It sounds like the bad state is triggered when Apache hits a timeout,
and we hit that timeout because the system is slow or busy. We could try
to make things less slow, but would it work equally well to increase
that timeout?

-Peff

Re: [RFH] Why do osx CI jobs so unreliable?

[Patrick Steinhardt]

On Fri, Jun 26, 2026 at 01:16:57AM -0400, Jeff King wrote:
> On Thu, Jun 25, 2026 at 08:27:35PM -0700, Michael Montalbo wrote:
> 
> > I think that is the trigger for issues we've been seeing. I spent
> > some time investigating the Apache side over the last week and maybe
> > found a mod_http2 bug, which I filed upstream with a potential fix:
> > 
> >   bug:  https://bz.apache.org/bugzilla/show_bug.cgi?id=70131
> >   fix:  https://github.com/mmontalbo/httpd/pull/2
> 
> Thanks both of you for digging into this. I'm not familiar enough with
> Apache's code to pass confident judgement, but your findings certainly
> convinced me that this is just an apache bug.

The bug manifests both with HTTP/1.1 and HTTP/2 though, so this wouldn't
fully fix the flakes we see, right?

> > Given there could be a potential reliability issue with an upstream
> > dependency like Apache, I was considering what mitigation strategies
> > might help:
> > [...]
> 
> Depending on how widespread the Apache bug is, another option might just
> be: do nothing and wait for it to get fixed.
> 
> Trying to make the wedged state fail fast and loudly is mostly just
> punting on the problem. We'd still see spurious failures. We've so far
> resisted the urge to do any automatic flaky-test retries, preferring
> instead to just try to root out the flakes. I'm a little hesitant to
> start now, because I think our strategy has mostly been good so far, and
> I've seen some horrible counter-examples where flakes and retries become
> a routine drag on development (and I'm afraid that accommodating flakes
> might make them more common).

I agree. I'm not a fan of retry logic, as every flaky test may mask an
actual bug that we haven't fully investigated yet.

> >   - Make slow tests faster by optimizing the test itself and/or
> >     the test runner configuration (e.g., job number matching
> >     cores) so wedges become less likely.
> 
> It sounds like the bad state is triggered when Apache hits a timeout,
> and we hit that timeout because the system is slow or busy. We could try
> to make things less slow, but would it work equally well to increase
> that timeout?

I was also wondering whether we can maybe work around the issue by
increasing the Apache timeout value. That sounds like an easy potential
solution to try, and from all we've discovered so far it doesn't feel
like this is something we can address on the Git side.

Patrick

Re: [RFH] Why do osx CI jobs so unreliable?

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

>> Trying to make the wedged state fail fast and loudly is mostly just
>> punting on the problem. We'd still see spurious failures. We've so far
>> resisted the urge to do any automatic flaky-test retries, preferring
>> instead to just try to root out the flakes. I'm a little hesitant to
>> start now, because I think our strategy has mostly been good so far, and
>> I've seen some horrible counter-examples where flakes and retries become
>> a routine drag on development (and I'm afraid that accommodating flakes
>> might make them more common).
>
> I agree. I'm not a fan of retry logic, as every flaky test may mask an
> actual bug that we haven't fully investigated yet.

Can't agree more.

> I was also wondering whether we can maybe work around the issue by
> increasing the Apache timeout value. That sounds like an easy potential
> solution to try, and from all we've discovered so far it doesn't feel
> like this is something we can address on the Git side.

Thanks, all, for looking into this.

Re: [RFH] Why do osx CI jobs so unreliable?

[Michael Montalbo]

On Fri, Jun 26, 2026 at 3:50 AM Patrick Steinhardt <ps@pks.im> wrote:
> The bug manifests both with HTTP/1.1 and HTTP/2 though, so this wouldn't
> fully fix the flakes we see, right?

Yes you are right. The linked fix would just prevent the hanging after timeout
for HTTP/2 tests, but still leaves HTTP/1.1 fakes.

> I was also wondering whether we can maybe work around the issue by
> increasing the Apache timeout value. That sounds like an easy potential
> solution to try, and from all we've discovered so far it doesn't feel
> like this is something we can address on the Git side.

I think Peff and Patrick's suggestion to just increase the Apache timeout
makes sense. I ran some experiments using a really long timeout with an
artificially slowed down CI runner and all the jobs made progress
(if slowly) without stalling, and eventually completed successfully:

https://github.com/mmontalbo/git/actions/runs/28267019651

I haven't spent a lot of time trying to figure out what the right timeout
value should be. An hour definitely seems like overkill, with something
on the order of 5-10 minutes seeming more reasonable, but I don't
have a principled number.

[PATCH 0/3] fixing expensive http test timeouts

[Jeff King]

On Fri, Jun 26, 2026 at 04:26:28PM -0700, Michael Montalbo wrote:

> I think Peff and Patrick's suggestion to just increase the Apache timeout
> makes sense. I ran some experiments using a really long timeout with an
> artificially slowed down CI runner and all the jobs made progress
> (if slowly) without stalling, and eventually completed successfully:
> 
> https://github.com/mmontalbo/git/actions/runs/28267019651
> 
> I haven't spent a lot of time trying to figure out what the right timeout
> value should be. An hour definitely seems like overkill, with something
> on the order of 5-10 minutes seeming more reasonable, but I don't
> have a principled number.

Here are some patches to keep things moving along. I arbitrarily picked
10 minutes, because multiplying the 1-minute default by 10 felt right. ;)

The first one just bumps the timeout and should make our problems go
away. The other two are optimizations, but I'm on the fence on whether
the final patch is worth it.

Thanks again for all of the digging.

  [1/3]: t/lib-httpd: bump apache timeout
  [2/3]: t5551: put many-tags case into its own repo
  [3/3]: t5551: pack refs after creating many tags

 t/lib-httpd/apache.conf     |  1 +
 t/t5551-http-fetch-smart.sh | 10 ++++++----
 2 files changed, 7 insertions(+), 4 deletions(-)

-Peff

[PATCH 1/3] t/lib-httpd: bump apache timeout

[Jeff King]

Since enabling more tests with 7a094d68a2 (ci: run expensive tests on
push builds to integration branches, 2026-05-08), we sometimes see test
failures or timeouts in GitHub CI. The culprit seems to be the "enormous
ref negotiation" test in t5551, which creates ~100k tag refs in our http
server-side repo.

Iterating through the loose refs of this repo to generate a ref
advertisement can take a long time, especially on a platform with slow
I/O. On my otherwise unloaded local machine, a cold cache ref
advertisement takes ~10s. On a busy CI machine running tests in
parallel, it can presumably top 60s, which runs afoul of Apache's
default CGI timeout.

The result in t5551 is a test failure, where Apache simply hangs up the
connection and the client reports an error. But worse, t5559 runs the
same test with HTTP/2, and a bug in Apache causes the connection to hang
indefinitely! We eventually see this as a CI timeout after 6 hours.

Let's bump Apache's timeout to something much larger: 600 seconds. This
doesn't eliminate the possibility of a timeout, but it makes it much
less likely. It should eliminate both the test failures and the CI
timeouts in practice, and it protects us from running into similar
problems with other tests in the future.

There are two counter-arguments to consider.

One, could/should we just make the test faster? Probably yes. The
biggest mistake here is having such an absurd number of unpacked refs on
a system which is bottle-necked on I/O. But I think it's worth bumping
the timeout so that we can fix this (and possibly other) correctness
issues, and then consider performance separately (which we'll do in
subsequent patches).

And two, is this just papering over a problem that users might see in
the real world? We could teach Git to handle this case more gracefully
with optimizations or keep-alives. But I think it's really an artificial
situation. You need a combination of this silly number of loose refs,
plus a very heavily loaded system. If you were trying to run a real
server and it took more than 60s to generate the ref advertisement, I
don't think the timeout is your biggest problem. Your crappy service is,
and you should adjust your resources to match your load. I.e., it is
probably reasonable for Git to assume that advertisements happen
fast-ish and don't need protocol-level keepalives.

Though the patch here is small, tons of work went into analyzing the
problem. Many thanks to the contributors credited below.

Helped-by: Michael Montalbo <mmontalbo@gmail.com>
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Jeff King <peff@peff.net>
---
I didn't reference Michael's bugzilla report directly, because you can't
read it without a login. :(

Maybe it's worth doing anyway?

 t/lib-httpd/apache.conf | 1 +
 1 file changed, 1 insertion(+)

diff --git a/t/lib-httpd/apache.conf b/t/lib-httpd/apache.conf
index 40a690b0bb..4149fc1078 100644
--- a/t/lib-httpd/apache.conf
+++ b/t/lib-httpd/apache.conf
@@ -4,6 +4,7 @@ DocumentRoot www
 LogFormat "%h %l %u %t \"%r\" %>s %b" common
 CustomLog access.log common
 ErrorLog error.log
+Timeout 600
 <IfModule !mod_log_config.c>
 	LoadModule log_config_module modules/mod_log_config.so
 </IfModule>
-- 
2.55.0.rc2.353.gf769b6597e

Re: [PATCH 1/3] t/lib-httpd: bump apache timeout

[Michael Montalbo]

On Sun, Jun 28, 2026 at 1:00 AM Jeff King <peff@peff.net> wrote:
>
> I didn't reference Michael's bugzilla report directly, because you can't
> read it without a login. :(
>
> Maybe it's worth doing anyway?
>

I also thought the report being behind a login was unfortunate. For the
historical record, I ended up submitting a patch[1] to their public GitHub
mirror that describes the issue in more detail.

[1] https://github.com/apache/httpd/pull/676

[PATCH 2/3] t5551: put many-tags case into its own repo

[Jeff King]

Most of the t5551 http fetch tests use a handful of refs. But there are
a few test cases which check our handling of large numbers of refs.
These tests use the same server-side repo, so all subsequent tests end
up having to consider those extra refs, too.

The result is that the test script is a bit slower than it needs to be.
In a normal run, moving the "2,000 tags" test into its own repo drops my
runtime for the whole script from ~2.7s to ~1.9s.

This is a modest gain, but when we add the "--long" flag it gets much
bigger. There we trigger a test (marked with EXPENSIVE) that adds
100,000 tags, and the script runtime jumps to ~95s. But if we use the
same "many tags" repo for that, our runtime drops to just ~37s.

This is a pretty easy win to drop the cost of the script. It may even be
a larger gain on a heavily loaded system, since one of the main costs
here is unpacked refs, which are heavy on system time and I/O costs.

It's possible we are reducing test coverage, since all of those other
tests were inadvertently using large ref advertisements (and thus could
have uncovered some unexpected interaction). But that seems somewhat
unlikely; the tests targeted at the large number of refs are doing
roughly similar things to the other tests.

Note that the real performance culprit is the 100k-tag --long test, not
the 2k-tag one. So we could just let the 100k one use its own repo, and
keep the 2k tags in the main repo. But since these two tests are
somewhat interlinked, it's easier to just move them both (and it does
provide a small gain even for the 2000-tag test). I also notice that the
2000-tag test is gated on the CMDLINE_LIMIT prereq, and without that the
later EXPENSIVE test will fail (since we won't have a too-many-refs
clone). Nobody seems to have noticed or complained after many years, and
I left it alone for this patch.

Signed-off-by: Jeff King <peff@peff.net>
---
 t/t5551-http-fetch-smart.sh | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
index e236e526f0..cd851f24b8 100755
--- a/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@ -397,15 +397,16 @@ create_tags () {
 }
 
 test_expect_success 'create 2,000 tags in the repo' '
+	git init "$HTTPD_DOCUMENT_ROOT_PATH/many-tags.git" &&
 	(
-		cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+		cd "$HTTPD_DOCUMENT_ROOT_PATH/many-tags.git" &&
 		create_tags 1 2000
 	)
 '
 
 test_expect_success CMDLINE_LIMIT \
 	'clone the 2,000 tag repo to check OS command line overflow' '
-	run_with_limited_cmdline git clone $HTTPD_URL/smart/repo.git too-many-refs &&
+	run_with_limited_cmdline git clone $HTTPD_URL/smart/many-tags.git too-many-refs &&
 	(
 		cd too-many-refs &&
 		git for-each-ref refs/tags >actual &&
@@ -483,12 +484,12 @@ test_expect_success 'test allowanysha1inwant with unreachable' '
 test_expect_success EXPENSIVE 'http can handle enormous ref negotiation' '
 	test_when_finished "rm -f tags" &&
 	(
-		cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+		cd "$HTTPD_DOCUMENT_ROOT_PATH/many-tags.git" &&
 		create_tags 2001 50000
 	) &&
 	git -C too-many-refs fetch -q --tags &&
 	(
-		cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+		cd "$HTTPD_DOCUMENT_ROOT_PATH/many-tags.git" &&
 		create_tags 50001 100000
 	) &&
 	git -C too-many-refs fetch -q --tags &&
-- 
2.55.0.rc2.353.gf769b6597e

Re: [PATCH 2/3] t5551: put many-tags case into its own repo

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

> diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
> index e236e526f0..cd851f24b8 100755
> --- a/t/t5551-http-fetch-smart.sh
> +++ b/t/t5551-http-fetch-smart.sh
> @@ -397,15 +397,16 @@ create_tags () {
>  }
>  
>  test_expect_success 'create 2,000 tags in the repo' '
> +	git init "$HTTPD_DOCUMENT_ROOT_PATH/many-tags.git" &&
>  	(
> -		cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
> +		cd "$HTTPD_DOCUMENT_ROOT_PATH/many-tags.git" &&
>  		create_tags 1 2000
>  	)
>  '

While all the other repositories used in this tests are bare
repositories, this new one is a non-bare repository.

It shouldn't make any difference, but since I noticed it...

Re: [PATCH 2/3] t5551: put many-tags case into its own repo

[Jeff King]

On Sun, Jun 28, 2026 at 02:44:32PM -0700, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> > diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
> > index e236e526f0..cd851f24b8 100755
> > --- a/t/t5551-http-fetch-smart.sh
> > +++ b/t/t5551-http-fetch-smart.sh
> > @@ -397,15 +397,16 @@ create_tags () {
> >  }
> >  
> >  test_expect_success 'create 2,000 tags in the repo' '
> > +	git init "$HTTPD_DOCUMENT_ROOT_PATH/many-tags.git" &&
> >  	(
> > -		cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
> > +		cd "$HTTPD_DOCUMENT_ROOT_PATH/many-tags.git" &&
> >  		create_tags 1 2000
> >  	)
> >  '
> 
> While all the other repositories used in this tests are bare
> repositories, this new one is a non-bare repository.
> 
> It shouldn't make any difference, but since I noticed it...

Ah, yeah. It should work either way, but it is slightly confusing for it
to be non-bare. I'll wait to re-send (though if nothing else comes up,
it may be simpler for you to just amend on your side).

-Peff

Re: [PATCH 2/3] t5551: put many-tags case into its own repo

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

> On Sun, Jun 28, 2026 at 02:44:32PM -0700, Junio C Hamano wrote:
>
>> Jeff King <peff@peff.net> writes:
>> 
>> > diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
>> > index e236e526f0..cd851f24b8 100755
>> > --- a/t/t5551-http-fetch-smart.sh
>> > +++ b/t/t5551-http-fetch-smart.sh
>> > @@ -397,15 +397,16 @@ create_tags () {
>> >  }
>> >  
>> >  test_expect_success 'create 2,000 tags in the repo' '
>> > +	git init "$HTTPD_DOCUMENT_ROOT_PATH/many-tags.git" &&
>> >  	(
>> > -		cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
>> > +		cd "$HTTPD_DOCUMENT_ROOT_PATH/many-tags.git" &&
>> >  		create_tags 1 2000
>> >  	)
>> >  '
>> 
>> While all the other repositories used in this tests are bare
>> repositories, this new one is a non-bare repository.
>> 
>> It shouldn't make any difference, but since I noticed it...
>
> Ah, yeah. It should work either way, but it is slightly confusing for it
> to be non-bare. I'll wait to re-send (though if nothing else comes up,
> it may be simpler for you to just amend on your side).

OK.  It seems both Patrick and you are in favor of using only [1/3]
& [2/3] but dropping [3/3]?  If that is the concensus I can just
tweak this one and apply before 2.55 final.

Thanks.

Re: [PATCH 2/3] t5551: put many-tags case into its own repo

[Jeff King]

On Mon, Jun 29, 2026 at 07:42:31AM -0700, Junio C Hamano wrote:

> > Ah, yeah. It should work either way, but it is slightly confusing for it
> > to be non-bare. I'll wait to re-send (though if nothing else comes up,
> > it may be simpler for you to just amend on your side).
> 
> OK.  It seems both Patrick and you are in favor of using only [1/3]
> & [2/3] but dropping [3/3]?  If that is the concensus I can just
> tweak this one and apply before 2.55 final.

Yep, that sounds great. Looks like it already happened. :)

-Peff

[PATCH 3/3] t5551: pack refs after creating many tags

[Jeff King]

We have two tests that create 2,000 and 100,000 tags respectively.
After doing so, the resulting state can be a bit slow to work with when
using the "files" ref backend, as each of those refs is in its own file.

This isn't a very realistic scenario, as we'd expect most of those refs
to be packed. If they accrue over time along with objects, they'd get
packed by maintenance/gc runs. And if you have a process that creates a
ton of refs at once (like a big fast-import), the usual recommendation
is to run maintenance afterwards.

So let's follow that recommendation and pack the refs ourselves.
Unfortunately, this does not seem to produce an improvement to the
run-time of the test script! That's because after producing this state,
we perform only a few fetches of it. And packing the refs costs at least
as much as serving a ref advertisement (both have to iterate the refs,
but packing additionally must write .lock files as we pack).

My wall-clock time was slightly improved (but within the noise) with
this patch, but my user and system CPU time were slightly worse!
However, on a loaded system with I/O bottlenecks, it may be a net win.
That's somewhat of a guess, though.

It would be nice if we had a way to generate all of these refs without
writing so many individual files. But even if we taught the ref code to
write large cases directly to the packed-refs file, we'd still need to
take individual locks. The real solution is a backend like reftable,
which shaves ~30% off of the test runtime.

Signed-off-by: Jeff King <peff@peff.net>
---
I'm iffy on whether this one is worth it.

If you apply just this patch without patch 2, then the run-time does
improve quite a bit. The cost of packing is amortized by the improved
performance for all of those subsequent tests (but after patch 2, they
never even see the unpacked state).

Likewise, I suspect this would make our timeout problems go away even
without patch 1.

So the whole series _could_ be reduced to just this one patch. But
hopefully the reasoning given in the earlier patches makes sense, at
which point this one is kind of superfluous.

 t/t5551-http-fetch-smart.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
index cd851f24b8..e2e729216f 100755
--- a/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@ -393,6 +393,7 @@ create_tags () {
 	tag=$(perl -e "print \"bla\" x 30") &&
 	sed -e "s|^:\([^ ]*\) \(.*\)$|create refs/tags/$tag-\1 \2|" <marks >input &&
 	git update-ref --stdin <input &&
+	git pack-refs --all &&
 	rm input
 }
 
-- 
2.55.0.rc2.353.gf769b6597e

Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

> So let's follow that recommendation and pack the refs ourselves.
> Unfortunately, this does not seem to produce an improvement to the
> run-time of the test script! That's because after producing this state,
> we perform only a few fetches of it. And packing the refs costs at least
> as much as serving a ref advertisement (both have to iterate the refs,
> but packing additionally must write .lock files as we pack).

Testing a pathological set-up with too many loose refs may have
extra value, as long as we are also testing the recommended set-up,
so ideally we should have both ;-) but if we have to pick only one
and drop the other, we probably should be testing the packed case.

> I'm iffy on whether this one is worth it.

I am ambivalent, too, about this change for the purpose of the
"yeek, apache times out while enumerating refs" issue.  But see
above ;-)

Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Patrick Steinhardt]

On Sun, Jun 28, 2026 at 04:07:10AM -0400, Jeff King wrote:
> We have two tests that create 2,000 and 100,000 tags respectively.
> After doing so, the resulting state can be a bit slow to work with when
> using the "files" ref backend, as each of those refs is in its own file.
> 
> This isn't a very realistic scenario, as we'd expect most of those refs
> to be packed. If they accrue over time along with objects, they'd get
> packed by maintenance/gc runs. And if you have a process that creates a
> ton of refs at once (like a big fast-import), the usual recommendation
> is to run maintenance afterwards.
> 
> So let's follow that recommendation and pack the refs ourselves.
> Unfortunately, this does not seem to produce an improvement to the
> run-time of the test script! That's because after producing this state,
> we perform only a few fetches of it. And packing the refs costs at least
> as much as serving a ref advertisement (both have to iterate the refs,
> but packing additionally must write .lock files as we pack).

> My wall-clock time was slightly improved (but within the noise) with
> this patch, but my user and system CPU time were slightly worse!
> However, on a loaded system with I/O bottlenecks, it may be a net win.
> That's somewhat of a guess, though.
> 
> It would be nice if we had a way to generate all of these refs without
> writing so many individual files. But even if we taught the ref code to
> write large cases directly to the packed-refs file, we'd still need to
> take individual locks. The real solution is a backend like reftable,
> which shaves ~30% off of the test runtime.

We kind of already have this with the `REF_TRANSACTION_FLAG_INITIAL`
flag, but right now it is only used when performing a clone or when
migrating references. Also, it requires an empty repository that has no
references yet.

It raises the question whether we could also extend git-fast-import(1)
to use it, as it would typically be run on an almost-empty repository.
It's the "almost" that kills it though, as we already do have at least
the HEAD reference. So it could be feasible, but it's not as trivial as
just setting the flag and then we're magically faster.

And besides, in this particular test here we run git-fast-import(1)
multiple times in the same repository, so it wouldn't help us.

We could of course extend all of this so that Git is able to write into
the packed-refs directly, even with preexisting refs. But I agree with
your sentiment: it doesn't feel worth it as the reftable backend fixes
scenarios like this anyway.

> Signed-off-by: Jeff King <peff@peff.net>
> ---
> I'm iffy on whether this one is worth it.
> 
> If you apply just this patch without patch 2, then the run-time does
> improve quite a bit. The cost of packing is amortized by the improved
> performance for all of those subsequent tests (but after patch 2, they
> never even see the unpacked state).
> 
> Likewise, I suspect this would make our timeout problems go away even
> without patch 1.
> 
> So the whole series _could_ be reduced to just this one patch. But
> hopefully the reasoning given in the earlier patches makes sense, at
> which point this one is kind of superfluous.

Agreed. I'd just merge the first two patches and drop this one here.

Thanks!

Patrick

Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Jeff King]

On Mon, Jun 29, 2026 at 07:57:21AM +0200, Patrick Steinhardt wrote:

> > It would be nice if we had a way to generate all of these refs without
> > writing so many individual files. But even if we taught the ref code to
> > write large cases directly to the packed-refs file, we'd still need to
> > take individual locks. The real solution is a backend like reftable,
> > which shaves ~30% off of the test runtime.
> 
> We kind of already have this with the `REF_TRANSACTION_FLAG_INITIAL`
> flag, but right now it is only used when performing a clone or when
> migrating references. Also, it requires an empty repository that has no
> references yet.
> 
> It raises the question whether we could also extend git-fast-import(1)
> to use it, as it would typically be run on an almost-empty repository.
> It's the "almost" that kills it though, as we already do have at least
> the HEAD reference. So it could be feasible, but it's not as trivial as
> just setting the flag and then we're magically faster.
> 
> And besides, in this particular test here we run git-fast-import(1)
> multiple times in the same repository, so it wouldn't help us.
> 
> We could of course extend all of this so that Git is able to write into
> the packed-refs directly, even with preexisting refs. But I agree with
> your sentiment: it doesn't feel worth it as the reftable backend fixes
> scenarios like this anyway.

Yup. In the past I've pondered exposing this via update-ref, but I think
it's too weird and/or dangerous to do so. Especially because you are
still stuck creating all of the .lock files, so the performance is not
even that much better (though it does save you doing so _twice_ when you
then pack the refs).

So the performance option you really want is "YOLO, just write some
packed-refs without locking". But that is not something I think we want
to expose to users. ;)

We could do it ad-hoc within this test like so:

diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
index dcff0bc7d4..276c7ac002 100755
--- a/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@ -389,11 +389,15 @@ create_tags () {
 		echo "from :$1"
 	done | git fast-import --export-marks=marks &&
 
+	# should be mostly a noop, but makes sure we have the right header
+	git pack-refs &&
+
 	# now assign tags to all the dangling commits we created above
+	# It is OK to write directly to the packed-refs file because we know
+	# that our entries are sorted by refname, and that they all
+	# come after what we wrote earlier.
 	tag=$(perl -e "print \"bla\" x 30") &&
-	sed -e "s|^:\([^ ]*\) \(.*\)$|create refs/tags/$tag-\1 \2|" <marks >input &&
-	git update-ref --stdin <input &&
-	rm input
+	sed -e "s|^:\([^ ]*\) \(.*\)$|\2 refs/tags/$tag-\1|" <marks >>packed-refs
 }
 
 test_expect_success 'create 2,000 tags in the repo' '

That gives us the same ~30% speedup that using reftables does, but it
still is quite gross and fragile. And it is not even strictly correct,
because we don't zero-pad the numbered tags (so our file is subtly out
of order).  Plus it would need to be conditional on the ref backend
being used. Yuck.


There's one other thing you might find interesting. While poking at the
timings here the other day, I noticed that reftable is very eager to
stat the tables.list file. Try this:

  git init --ref-format=reftable
  blob=$(echo foo | git hash-object -w --stdin)
  seq -f "create refs/tags/foo-%g $blob" 2000 |
  strace -c git update-ref --stdin

We make 2000 fstat, which strace claims takes 85% of the time. I suspect
this is over-emphasized because strace inherently makes syscalls slow,
but running with perf also highlights it as a non-trivial cost.

It has been a long time since I've thought about reftable internals, but
it feels like we ought to be able to take the lock and then trust that
the stack has not been manipulated.

It may not be worth digging into too much, though. I can make 50,000
refs in 150ms on my system, which is probably good enough (especially
compared to the files backend).

-Peff

Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Patrick Steinhardt]

On Mon, Jun 29, 2026 at 04:35:27PM -0400, Jeff King wrote:
> There's one other thing you might find interesting. While poking at the
> timings here the other day, I noticed that reftable is very eager to
> stat the tables.list file. Try this:
> 
>   git init --ref-format=reftable
>   blob=$(echo foo | git hash-object -w --stdin)
>   seq -f "create refs/tags/foo-%g $blob" 2000 |
>   strace -c git update-ref --stdin
> 
> We make 2000 fstat, which strace claims takes 85% of the time. I suspect
> this is over-emphasized because strace inherently makes syscalls slow,
> but running with perf also highlights it as a non-trivial cost.

Yeah, this rings a bell. If I remember correctly, this is because we
call `refs_resolve_ref_unsafe()` to verify whether the target already
exists. And as that function is generic, it wasn't easy to optimize it
by reusing the already-loaded reftable stack.

> It has been a long time since I've thought about reftable internals, but
> it feels like we ought to be able to take the lock and then trust that
> the stack has not been manipulated.

Yeah, that would certainly be an option to explore.

> It may not be worth digging into too much, though. I can make 50,000
> refs in 150ms on my system, which is probably good enough (especially
> compared to the files backend).

True, it's going to be much better compared to the "files" backend. But
that isn't enough reason to not optimize it even further -- doubly so if
it actually takes 85% of the time. Sounds like a low-hanging fruit to me
that can result in a significant speedup.

I'll probably not get to it anytime soon, but I'll create an issue to
keep track of it.

Patrick

Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Jeff King]

On Tue, Jun 30, 2026 at 11:05:22AM +0200, Patrick Steinhardt wrote:

> > We make 2000 fstat, which strace claims takes 85% of the time. I suspect
> > this is over-emphasized because strace inherently makes syscalls slow,
> > but running with perf also highlights it as a non-trivial cost.
> 
> Yeah, this rings a bell. If I remember correctly, this is because we
> call `refs_resolve_ref_unsafe()` to verify whether the target already
> exists. And as that function is generic, it wasn't easy to optimize it
> by reusing the already-loaded reftable stack.

I think it's similar to that. I dug down and got some actual performance
numbers below for eliminating the fstat() calls, with the conclusion
that it's probably not worth spending too much time digging into it. But
details below for completeness.

I was wrong to say fstat() before, it's a regular stat(). The
interesting backtrace is:

  #0  __GI___stat64 (file=0x555555ab0bf0 "/home/peff/tmp/.git/reftable/tables.list", buf=0x7fffffffd630)
      at ../sysdeps/unix/sysv/linux/stat64.c:29
  #1  0x0000555555832ad6 in stack_uptodate (st=0x555555ab0ae0) at reftable/stack.c:575
  #2  0x0000555555832c5c in reftable_stack_reload (st=0x555555ab0ae0) at reftable/stack.c:625
  #3  0x000055555581f690 in backend_for (out=0x7fffffffd798, store=0x555555ab0900,
      refname=0x555555aae178 "refs/tags/foo-1", rewritten_ref=0x7fffffffd780, reload=1) at refs/reftable-backend.c:283
  #4  0x0000555555824957 in reftable_be_reflog_exists (ref_store=0x555555ab0900,
      refname=0x555555aae178 "refs/tags/foo-1") at refs/reftable-backend.c:2266
  #5  0x000055555581393a in refs_reflog_exists (refs=0x555555ab0900, refname=0x555555aae178 "refs/tags/foo-1")
      at refs.c:2995
  #6  0x000055555581f730 in should_write_log (refs=0x555555ab0900, refname=0x555555aae178 "refs/tags/foo-1")
      at refs/reftable-backend.c:301
  #7  0x00005555558224df in write_transaction_table (writer=0x5555569abe30, cb_data=0x5555569ab820)
      at refs/reftable-backend.c:1511
  #8  0x000055555583354d in reftable_addition_add (add=0x5555569ab050,
      write_table=0x5555558220f0 <write_transaction_table>, arg=0x5555569ab820) at reftable/stack.c:902
  #9  0x0000555555822b2b in reftable_be_transaction_finish (ref_store=0x555555ab0900, transaction=0x555555ab0c80,
      err=0x7fffffffdbc0) at refs/reftable-backend.c:1633
  #10 0x0000555555813161 in ref_transaction_commit (transaction=0x555555ab0c80, err=0x7fffffffdbc0) at refs.c:2769
  #11 0x00005555556956c9 in update_refs_stdin (flags=0) at builtin/update-ref.c:789

So we are asking about reflogs for each ref under the "only reflog if a
log already exists" rule. Which means we can easily disable it by
setting core.logallrefupdates to "always", giving us a way to measure
the impact. So we can try:

  git init --ref-format=reftable
  blob=$(echo foo | git hash-object -w --stdin)
  seq -f "create refs/tags/foo-%g $blob" 50000 >input
  cp -a .git/reftable reftable.orig
  hyperfine \
  	-p 'rm -rf .git/reftable; cp -a reftable.orig .git/reftable' \
  	-L config true,always \
  	'git -c core.logallrefupdates={config} update-ref --stdin <input'

which yields:

  Benchmark 1: git -c core.logallrefupdates=true update-ref --stdin <input
    Time (mean ± σ):     128.8 ms ±   1.5 ms    [User: 97.1 ms, System: 31.7 ms]
    Range (min … max):   126.4 ms … 131.3 ms    23 runs
  
  Benchmark 2: git -c core.logallrefupdates=always update-ref --stdin <input
    Time (mean ± σ):     195.2 ms ±   1.7 ms    [User: 182.1 ms, System: 13.0 ms]
    Range (min … max):   191.9 ms … 197.6 ms    15 runs

So we saved all of those stat() calls, but writing the actual reflog
entries adds much more cost!

Sadly there is no "never" option for core.logallrefupdates. I hacked one
in and the result took ~96ms to run. So that tells us the cost of the
stat() checks: around 25% of the runtime.

Which is a big-ish percentage, but a small absolute number. It's 0.64us
per ref. Perhaps not worrying about too much.

The other interesting thing I noticed is that we seem to write() entries
individually with no buffering. Probably we could get an easy speedup
for big cases like this by using stdio in the fd_writer abstraction.
We're again pinching pennies to some degree, but I expect we may be able
to drop the 120ms case down to 60ms or so (just guessing based on the
extra reflog writes adding ~70ms).

There was one other oddity I didn't quite resolve. You may notice the
gross reftable.orig stuff in hyperfine. I originally wrote this as:

    git for-each-ref --format="delete %(refname)" | git update-ref --stdin

but for some reason that causes the subsequent update-ref to loop
infinitely on merged_iter_next_entry(). It does so reliably, but I can't
reproduce it outside of hyperfine. Super weird, and I'm sure I'm missing
something obvious.

-Peff

weird quadratic reftable behavior, was: Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Jeff King]

On Tue, Jun 30, 2026 at 07:47:02PM -0400, Jeff King wrote:

> There was one other oddity I didn't quite resolve. You may notice the
> gross reftable.orig stuff in hyperfine. I originally wrote this as:
> 
>     git for-each-ref --format="delete %(refname)" | git update-ref --stdin
> 
> but for some reason that causes the subsequent update-ref to loop
> infinitely on merged_iter_next_entry(). It does so reliably, but I can't
> reproduce it outside of hyperfine. Super weird, and I'm sure I'm missing
> something obvious.

Ah, maybe not infinite, but probably quadratic. The key is that you have
to delete a lot of refs and then try to insert them again. So with this
script:

  nr=$1; shift
  rm -rf .git
  
  git init --ref-format=reftable
  blob=$(echo foo | git hash-object -w --stdin)
  seq -f "create refs/tags/foo-%g $blob" $nr >input
  git update-ref --stdin <input
  git for-each-ref --format="delete %(refname)" | git update-ref --stdin
  time git update-ref --stdin <input

I get results like this:

  nr   | runtime
  ------------
  1000 | 0.125s
  2000 | 0.454s
  4000 | 1.811s
  8000 | 7.091s

So for every doubling of the input size, the runtime quadruples. I guess
it is iterating through some deleted tombstone entries, but I'm not sure
why.

That's probably a more interesting and productive performance problem to
work on than micro-optimizing out the last few microseconds of writing. :)

-Peff

Re: weird quadratic reftable behavior, was: Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Patrick Steinhardt]

On Tue, Jun 30, 2026 at 07:58:50PM -0400, Jeff King wrote:
> On Tue, Jun 30, 2026 at 07:47:02PM -0400, Jeff King wrote:
> 
> > There was one other oddity I didn't quite resolve. You may notice the
> > gross reftable.orig stuff in hyperfine. I originally wrote this as:
> > 
> >     git for-each-ref --format="delete %(refname)" | git update-ref --stdin
> > 
> > but for some reason that causes the subsequent update-ref to loop
> > infinitely on merged_iter_next_entry(). It does so reliably, but I can't
> > reproduce it outside of hyperfine. Super weird, and I'm sure I'm missing
> > something obvious.
> 
> Ah, maybe not infinite, but probably quadratic. The key is that you have
> to delete a lot of refs and then try to insert them again. So with this
> script:
> 
>   nr=$1; shift
>   rm -rf .git
>   
>   git init --ref-format=reftable
>   blob=$(echo foo | git hash-object -w --stdin)
>   seq -f "create refs/tags/foo-%g $blob" $nr >input
>   git update-ref --stdin <input
>   git for-each-ref --format="delete %(refname)" | git update-ref --stdin
>   time git update-ref --stdin <input
> 
> I get results like this:
> 
>   nr   | runtime
>   ------------
>   1000 | 0.125s
>   2000 | 0.454s
>   4000 | 1.811s
>   8000 | 7.091s
> 
> So for every doubling of the input size, the runtime quadruples. I guess
> it is iterating through some deleted tombstone entries, but I'm not sure
> why.
> 
> That's probably a more interesting and productive performance problem to
> work on than micro-optimizing out the last few microseconds of writing. :)

This is a known issue, I think [1].

The problem here is the tombstoning: when you delete all references,
chances are that they are not truly gone but that every reference is
just tombstoned. The problem with this is that reading refs may now take
signifciantly more time as we cannot just say "this stack is empty".
Instead, we need to figure out that it is empty by processing all the
tombstones, and that takes a lot of time.

I remember that I did some digging back then and improved the status quo
quite significantly by optimizing `refs_verify_refname_available()`. I'm
sure there are more opportunities for optimization here though -- I have
a feeling that we for example exhaust the merged iterator until its end
when searching for a specific refname, where we could easily abort once
the observed tombstone name sorts lexicographically after the needle.

But eventually I decided to not care too much about this edge case, as
it seems very specific to this artificial benchmark scenario. Which of
course doesn't mean that it's not worth doing, I just had bigger fish to
fry and didn't get around to it yet.

Patrick

[1]: <Z602dzQggtDdcgCX@tapette.crustytoothpaste.net>

Re: weird quadratic reftable behavior, was: Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Jeff King]

On Wed, Jul 01, 2026 at 08:17:45AM +0200, Patrick Steinhardt wrote:

> This is a known issue, I think [1].
> 
> The problem here is the tombstoning: when you delete all references,
> chances are that they are not truly gone but that every reference is
> just tombstoned. The problem with this is that reading refs may now take
> signifciantly more time as we cannot just say "this stack is empty".
> Instead, we need to figure out that it is empty by processing all the
> tombstones, and that takes a lot of time.
> 
> I remember that I did some digging back then and improved the status quo
> quite significantly by optimizing `refs_verify_refname_available()`. I'm
> sure there are more opportunities for optimization here though -- I have
> a feeling that we for example exhaust the merged iterator until its end
> when searching for a specific refname, where we could easily abort once
> the observed tombstone name sorts lexicographically after the needle.

Yeah, it is (mostly) the same problem. About half the time is spent in
refs_verify_refnames_available().

The other half is in reftable_be_transaction_prepare(). Looks like it
makes individual calls to prepare_single_update(), which reads each ref.
And those reads are expensive because of all of the tombstones. It might
be possible to do an iterator merge or similar between the sorted list
of transaction refs and the reftable contents.

> But eventually I decided to not care too much about this edge case, as
> it seems very specific to this artificial benchmark scenario. Which of
> course doesn't mean that it's not worth doing, I just had bigger fish to
> fry and didn't get around to it yet.

Yeah, that's fair. I dug a bit further in case there was anything useful
to write up, but I don't have much to add beyond what's here and in the
thread you linked. We can let it live on in the archive for now.

-Peff

Re: weird quadratic reftable behavior, was: Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Kristofer Karlsson]

On Wed, 1 Jul 2026 at 10:00, Jeff King <peff@peff.net> wrote:

> Yeah, it is (mostly) the same problem. About half the time is spent in
> refs_verify_refnames_available().
>
> The other half is in reftable_be_transaction_prepare(). Looks like it
> makes individual calls to prepare_single_update(), which reads each ref.
> And those reads are expensive because of all of the tombstones. It might
> be possible to do an iterator merge or similar between the sorted list
> of transaction refs and the reftable contents.

Hi, sorry for jumping in -- I found this interesting and started
poking at the code. I think both halves may share the same root
cause.

The merged iterator's suppress_deletions flag filters out tombstones
internally, which means higher-level code with prefix or refname
bounds never gets a chance to stop iteration early. By letting
tombstones pass through and filtering them one layer up in the
reftable backend, the existing bounds checks can kick in before
we scan through all the tombstones.

So instead of doing full scans inside merged_iter_next_void()
we can just delegate to merged_iter_next_entry() and instead
add a loop to reftable_be_reflog_exists() that skips
tombstones (but is amortized O(1)).

Now multiple call sites would need to add something like this
to compensate for returning tombstones:

    if (reftable_log_record_is_deletion(&iter->log))
        continue;

but it may be worth it if it reduces cost when there are many refs.

The key spot is reftable_ref_iterator_advance(), where the deletion
skip goes right after the existing prefix check -- so a tombstone
past the prefix stops iteration immediately instead of being
silently consumed. The same idea applies to reftable_backend_read_ref()
and the log iteration paths.

I have a local branch with this attempted fix. Rerunning the
benchmark:

  Before:
    nr=1000  0.306s
    nr=2000  0.945s
    nr=4000  3.816s
    nr=8000  14.93s

  After:
    nr=1000   0.020s
    nr=2000   0.044s
    nr=4000   0.071s
    nr=8000   0.145s
    nr=16000  0.258s
    nr=32000  0.591s

I can send a proper patch if needed/wanted, but I might have missed
something silly here.

Thanks,
Kristofer

Re: weird quadratic reftable behavior, was: Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Patrick Steinhardt]

On Wed, Jul 01, 2026 at 11:04:45AM +0200, Kristofer Karlsson wrote:
> On Wed, 1 Jul 2026 at 10:00, Jeff King <peff@peff.net> wrote:
> 
> > Yeah, it is (mostly) the same problem. About half the time is spent in
> > refs_verify_refnames_available().
> >
> > The other half is in reftable_be_transaction_prepare(). Looks like it
> > makes individual calls to prepare_single_update(), which reads each ref.
> > And those reads are expensive because of all of the tombstones. It might
> > be possible to do an iterator merge or similar between the sorted list
> > of transaction refs and the reftable contents.
> 
> Hi, sorry for jumping in -- I found this interesting and started
> poking at the code. I think both halves may share the same root
> cause.
> 
> The merged iterator's suppress_deletions flag filters out tombstones
> internally, which means higher-level code with prefix or refname
> bounds never gets a chance to stop iteration early. By letting
> tombstones pass through and filtering them one layer up in the
> reftable backend, the existing bounds checks can kick in before
> we scan through all the tombstones.

Ah, interesting. This kind of hits int o the direction that I proposed
of stopping iteration once we hit the first reference that has a
lexicographically-larget refname. But I thought about having to solve it
generically in the iterator somehow, and I wasn't really looking forward
to that.

Your solutions works around that issue indeed. It of course doesn't
solve reference iteration, which would still be expensive. But it does
solve the issue where we just want to look up a single reference, which
is what Peff noticed to be slow.

> So instead of doing full scans inside merged_iter_next_void()
> we can just delegate to merged_iter_next_entry() and instead
> add a loop to reftable_be_reflog_exists() that skips
> tombstones (but is amortized O(1)).
> 
> Now multiple call sites would need to add something like this
> to compensate for returning tombstones:
> 
>     if (reftable_log_record_is_deletion(&iter->log))
>         continue;
> 
> but it may be worth it if it reduces cost when there are many refs.

I think it certainly might be.

> The key spot is reftable_ref_iterator_advance(), where the deletion
> skip goes right after the existing prefix check -- so a tombstone
> past the prefix stops iteration immediately instead of being
> silently consumed. The same idea applies to reftable_backend_read_ref()
> and the log iteration paths.

Yup.

> I have a local branch with this attempted fix. Rerunning the
> benchmark:
> 
>   Before:
>     nr=1000  0.306s
>     nr=2000  0.945s
>     nr=4000  3.816s
>     nr=8000  14.93s
> 
>   After:
>     nr=1000   0.020s
>     nr=2000   0.044s
>     nr=4000   0.071s
>     nr=8000   0.145s
>     nr=16000  0.258s
>     nr=32000  0.591s
> 
> I can send a proper patch if needed/wanted, but I might have missed
> something silly here.

Nice gains. I certainly think it would make sense to polish this a bit
and then cast it into a patch.

Patrick

Re: weird quadratic reftable behavior, was: Re: [PATCH 3/3] t5551: pack refs after creating many tags

[Kristofer Karlsson]

On Wed, 1 Jul 2026 at 12:07, Patrick Steinhardt <ps@pks.im> wrote:
> >
> > I can send a proper patch if needed/wanted, but I might have missed
> > something silly here.
>
> Nice gains. I certainly think it would make sense to polish this a bit
> and then cast it into a patch.
>
> Patrick

I have a small draft here https://github.com/gitgitgadget/git/pull/2166
but I am honestly not sure if it's worth submitting as a patch - the
change is somewhat small, but spread out, and I failed to properly
reproduce the performance win in any realistic scenario (I had to
disable compaction to see the improvement).

I would want to rely on your expertise to know if this change
would be valuable to discuss as a patch at all.

Thanks,
Kristofer

Re: [PATCH 0/3] fixing expensive http test timeouts

[Patrick Steinhardt]

On Sun, Jun 28, 2026 at 03:57:16AM -0400, Jeff King wrote:
> On Fri, Jun 26, 2026 at 04:26:28PM -0700, Michael Montalbo wrote:
> 
> > I think Peff and Patrick's suggestion to just increase the Apache timeout
> > makes sense. I ran some experiments using a really long timeout with an
> > artificially slowed down CI runner and all the jobs made progress
> > (if slowly) without stalling, and eventually completed successfully:
> > 
> > https://github.com/mmontalbo/git/actions/runs/28267019651
> > 
> > I haven't spent a lot of time trying to figure out what the right timeout
> > value should be. An hour definitely seems like overkill, with something
> > on the order of 5-10 minutes seeming more reasonable, but I don't
> > have a principled number.
> 
> Here are some patches to keep things moving along. I arbitrarily picked
> 10 minutes, because multiplying the 1-minute default by 10 felt right. ;)
> 
> The first one just bumps the timeout and should make our problems go
> away. The other two are optimizations, but I'm on the fence on whether
> the final patch is worth it.
> 
> Thanks again for all of the digging.
> 
>   [1/3]: t/lib-httpd: bump apache timeout
>   [2/3]: t5551: put many-tags case into its own repo
>   [3/3]: t5551: pack refs after creating many tags

By the way, the only reason why we at GitLab haven't been feeling the
pain is that we only enable GIT_TEST_LONG for GitHub. So I was wondering
whether we want to have something like the below patch on top.

Patrick

diff --git a/ci/lib.sh b/ci/lib.sh
index b939110a6e..57801586aa 100755
--- a/ci/lib.sh
+++ b/ci/lib.sh
@@ -215,6 +215,14 @@ then
 	test macos != "$CI_OS_NAME" || CI_OS_NAME=osx
 	CI_REPO_SLUG="$GITHUB_REPOSITORY"
 	CI_JOB_ID="$GITHUB_RUN_ID"
+
+	case "$GITHUB_EVENT_NAME" in
+	pull_request)
+		CI_EVENT=pull_request;;
+	push)
+		CI_EVENT=push;;
+	esac
+
 	CC="${CC_PACKAGE:-${CC:-gcc}}"
 	DONT_SKIP_TAGS=t
 	handle_failed_tests () {
@@ -239,6 +247,13 @@ then
 	CI_BRANCH="$CI_COMMIT_REF_NAME"
 	CI_COMMIT="$CI_COMMIT_SHA"
 
+	case "$CI_PIPELINE_SOURCE" in
+	merge_request_event)
+		CI_EVENT=pull_request;;
+	push)
+		CI_EVENT=push;;
+	esac
+
 	case "$OS,$CI_JOB_IMAGE" in
 	Windows_NT,*)
 		CI_OS_NAME=windows
@@ -319,7 +334,7 @@ export SKIP_DASHED_BUILT_INS=YesPlease
 # enable "expensive" tests for PR events.
 # In order to catch bugs introduced at integration time by mismerges,
 # enable the long tests for pushes to the integration branches as well.
-case "$GITHUB_EVENT_NAME,$CI_BRANCH" in
+case "$CI_EVENT,$CI_BRANCH" in
 pull_request,*|push,*next*|push,*master*|push,*main*|push,*maint*)
 	export GIT_TEST_LONG=YesPlease
 	;;

Re: [PATCH 0/3] fixing expensive http test timeouts

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> By the way, the only reason why we at GitLab haven't been feeling the
> pain is that we only enable GIT_TEST_LONG for GitHub. So I was wondering
> whether we want to have something like the below patch on top.

If we can afford the cycles, it would be good to have similarly
larger coverage on two different platforms (compared to leaving one
of them not doing as much as the other when we know it).  On the
other hand, if we cannot cover _everything_ in one platform, it may
be a better use of the resources to have the other platform things
that are not covered already.  I see that among different pipeline
sources, we are doing TEST_LONG for pull requests to any branch, and
pushes only to "cast in stone" branches.  If there are other
branches that deserve to be tested with TEST_LONG upon other events
that the existing GitHub Actions CI does not trigger, it may be good
to have GitLab CI cover them, perhaps?





>
> Patrick
>
> diff --git a/ci/lib.sh b/ci/lib.sh
> index b939110a6e..57801586aa 100755
> --- a/ci/lib.sh
> +++ b/ci/lib.sh
> @@ -215,6 +215,14 @@ then
>  	test macos != "$CI_OS_NAME" || CI_OS_NAME=osx
>  	CI_REPO_SLUG="$GITHUB_REPOSITORY"
>  	CI_JOB_ID="$GITHUB_RUN_ID"
> +
> +	case "$GITHUB_EVENT_NAME" in
> +	pull_request)
> +		CI_EVENT=pull_request;;
> +	push)
> +		CI_EVENT=push;;
> +	esac
> +
>  	CC="${CC_PACKAGE:-${CC:-gcc}}"
>  	DONT_SKIP_TAGS=t
>  	handle_failed_tests () {
> @@ -239,6 +247,13 @@ then
>  	CI_BRANCH="$CI_COMMIT_REF_NAME"
>  	CI_COMMIT="$CI_COMMIT_SHA"
>  
> +	case "$CI_PIPELINE_SOURCE" in
> +	merge_request_event)
> +		CI_EVENT=pull_request;;
> +	push)
> +		CI_EVENT=push;;
> +	esac
> +
>  	case "$OS,$CI_JOB_IMAGE" in
>  	Windows_NT,*)
>  		CI_OS_NAME=windows
> @@ -319,7 +334,7 @@ export SKIP_DASHED_BUILT_INS=YesPlease
>  # enable "expensive" tests for PR events.
>  # In order to catch bugs introduced at integration time by mismerges,
>  # enable the long tests for pushes to the integration branches as well.
> -case "$GITHUB_EVENT_NAME,$CI_BRANCH" in
> +case "$CI_EVENT,$CI_BRANCH" in
>  pull_request,*|push,*next*|push,*master*|push,*main*|push,*maint*)
>  	export GIT_TEST_LONG=YesPlease
>  	;;

Re: [PATCH 0/3] fixing expensive http test timeouts

[Patrick Steinhardt]

On Mon, Jun 29, 2026 at 07:39:59AM -0700, Junio C Hamano wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> 
> > By the way, the only reason why we at GitLab haven't been feeling the
> > pain is that we only enable GIT_TEST_LONG for GitHub. So I was wondering
> > whether we want to have something like the below patch on top.
> 
> If we can afford the cycles, it would be good to have similarly
> larger coverage on two different platforms (compared to leaving one
> of them not doing as much as the other when we know it).  On the
> other hand, if we cannot cover _everything_ in one platform, it may
> be a better use of the resources to have the other platform things
> that are not covered already.  I see that among different pipeline
> sources, we are doing TEST_LONG for pull requests to any branch, and
> pushes only to "cast in stone" branches.  If there are other
> branches that deserve to be tested with TEST_LONG upon other events
> that the existing GitHub Actions CI does not trigger, it may be good
> to have GitLab CI cover them, perhaps?

I'm a bit hesitant to do such a split, mostly because the canonical
source of truth that the project typically uses is GitHub's CI. So I
want us at GitLab to be able to catch the same issues that GitHub would
flag. And if GitLab's CI stopped detecting everything that GitHub does,
then the result would likely be that we often create merge requests on
both platforms, which would only result in more wasted resources.

Patrick

Re: [PATCH 0/3] fixing expensive http test timeouts

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

>> pushes only to "cast in stone" branches.  If there are other
>> branches that deserve to be tested with TEST_LONG upon other events
>> that the existing GitHub Actions CI does not trigger, it may be good
>> to have GitLab CI cover them, perhaps?
>
> I'm a bit hesitant to do such a split, mostly because the canonical
> source of truth that the project typically uses is GitHub's CI. So I
> want us at GitLab to be able to catch the same issues that GitHub would
> flag. And if GitLab's CI stopped detecting everything that GitHub does,
> then the result would likely be that we often create merge requests on
> both platforms, which would only result in more wasted resources.

I didn't suggest splitting them into two circles that overlap but
each with area only it covers, though.  GitLab's coverage can be
superset to GitHub's and that would satify what I suggested.

FWIW, I do not consider GitHub's CI "the canonical source" at all.
It is a very handy service to use to check how well we are doing,
but from time to time it has its own hiccups ;-).

What can we do to make the visibility of GitLab's CI more prominent?

I know where the CI jobs that are triggered when I push out the
integration branches are found at GitHub's website[*], but I do not
think I know the corresponding one at GitLab, for example, and I
think that is a shame.


[Footnote]
 *1* I just made https://tinyurl.com/github-gitci that points at
     https://github.com/git/git/actions/workflows/main.yml?query=event%3Apush+actor%3Agitster

Re: [PATCH 0/3] fixing expensive http test timeouts

[Patrick Steinhardt]

On Mon, Jun 29, 2026 at 09:19:11AM -0700, Junio C Hamano wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> 
> >> pushes only to "cast in stone" branches.  If there are other
> >> branches that deserve to be tested with TEST_LONG upon other events
> >> that the existing GitHub Actions CI does not trigger, it may be good
> >> to have GitLab CI cover them, perhaps?
> >
> > I'm a bit hesitant to do such a split, mostly because the canonical
> > source of truth that the project typically uses is GitHub's CI. So I
> > want us at GitLab to be able to catch the same issues that GitHub would
> > flag. And if GitLab's CI stopped detecting everything that GitHub does,
> > then the result would likely be that we often create merge requests on
> > both platforms, which would only result in more wasted resources.
> 
> I didn't suggest splitting them into two circles that overlap but
> each with area only it covers, though.  GitLab's coverage can be
> superset to GitHub's and that would satify what I suggested.

Fair.

> FWIW, I do not consider GitHub's CI "the canonical source" at all.
> It is a very handy service to use to check how well we are doing,
> but from time to time it has its own hiccups ;-).

Well, GitLab of course has its own share of hiccups, like for example
the Chocolatey issues we've been facing.

> What can we do to make the visibility of GitLab's CI more prominent?
> 
> I know where the CI jobs that are triggered when I push out the
> integration branches are found at GitHub's website[*], but I do not
> think I know the corresponding one at GitLab, for example, and I
> think that is a shame.

The pipelines of the official mirror can be found at [1]. We might for
example add something like the below patch to our README.md to make it
more discoverable.

Patrick

[1]: https://gitlab.com/git-scm/git/-/pipelines

diff --git a/README.md b/README.md
index d87bca1b8c..9ad77fdf7e 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,5 @@
-[![Build status](https://github.com/git/git/workflows/CI/badge.svg)](https://github.com/git/git/actions?query=branch%3Amaster+event%3Apush)
+[![GitHub build status](https://github.com/git/git/workflows/CI/badge.svg)](https://github.com/git/git/actions?query=branch%3Amaster+event%3Apush)
+[![GitLab build status](https://gitlab.com/git-scm/git/badges/master/pipeline.svg)](https://gitlab.com/git-scm/git/-/pipelines?ref=master)
 
 Git - fast, scalable, distributed revision control system
 =========================================================

Re: [PATCH 0/3] fixing expensive http test timeouts

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> The pipelines of the official mirror can be found at [1]. We might for
> example add something like the below patch to our README.md to make it
> more discoverable.
>
> Patrick
>
> [1]: https://gitlab.com/git-scm/git/-/pipelines
>
> diff --git a/README.md b/README.md
> index d87bca1b8c..9ad77fdf7e 100644
> --- a/README.md
> +++ b/README.md
> @@ -1,4 +1,5 @@
> -[![Build status](https://github.com/git/git/workflows/CI/badge.svg)](https://github.com/git/git/actions?query=branch%3Amaster+event%3Apush)
> +[![GitHub build status](https://github.com/git/git/workflows/CI/badge.svg)](https://github.com/git/git/actions?query=branch%3Amaster+event%3Apush)
> +[![GitLab build status](https://gitlab.com/git-scm/git/badges/master/pipeline.svg)](https://gitlab.com/git-scm/git/-/pipelines?ref=master)
>  
>  Git - fast, scalable, distributed revision control system
>  =========================================================

Oh, nice.  We of course do not want to be heavily involved in
advertising offerings by commercial entities but I think these two
sites deserve one line each for their continued service to the
community ;-)

Re: [PATCH 0/3] fixing expensive http test timeouts

[Patrick Steinhardt]

On Tue, Jun 30, 2026 at 12:21:30PM -0700, Junio C Hamano wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> 
> > The pipelines of the official mirror can be found at [1]. We might for
> > example add something like the below patch to our README.md to make it
> > more discoverable.
> >
> > Patrick
> >
> > [1]: https://gitlab.com/git-scm/git/-/pipelines
> >
> > diff --git a/README.md b/README.md
> > index d87bca1b8c..9ad77fdf7e 100644
> > --- a/README.md
> > +++ b/README.md
> > @@ -1,4 +1,5 @@
> > -[![Build status](https://github.com/git/git/workflows/CI/badge.svg)](https://github.com/git/git/actions?query=branch%3Amaster+event%3Apush)
> > +[![GitHub build status](https://github.com/git/git/workflows/CI/badge.svg)](https://github.com/git/git/actions?query=branch%3Amaster+event%3Apush)
> > +[![GitLab build status](https://gitlab.com/git-scm/git/badges/master/pipeline.svg)](https://gitlab.com/git-scm/git/-/pipelines?ref=master)
> >  
> >  Git - fast, scalable, distributed revision control system
> >  =========================================================
> 
> Oh, nice.  We of course do not want to be heavily involved in
> advertising offerings by commercial entities but I think these two
> sites deserve one line each for their continued service to the
> community ;-)

Okay, I'll send a patch then. Thanks!

Patrick

Re: [RFH] Why do osx CI jobs so unreliable?

[Jeff King]

On Fri, Jun 26, 2026 at 12:50:17PM +0200, Patrick Steinhardt wrote:

> > Thanks both of you for digging into this. I'm not familiar enough with
> > Apache's code to pass confident judgement, but your findings certainly
> > convinced me that this is just an apache bug.
> 
> The bug manifests both with HTTP/1.1 and HTTP/2 though, so this wouldn't
> fully fix the flakes we see, right?

If I understand the situation correctly, there are really two problems.

First, the EXPENSIVE tests in t5551 sometimes trigger a timeout with
Apache's stock settings. This presumably became a problem recently due
to 7a094d68a2 (ci: run expensive tests on push builds to integration
branches, 2026-05-08). The same problem exists in t5559, which just
wraps t5551 but tells us to use http2.

This timeout will cause test failures in t5551, because we aren't able
to complete a request we expected to. Obviously bad and annoying.

The second problem is that when Apache hits the timeout in HTTP/2 mode,
it hangs forever. And then the CI job hangs for 6 hours until it's
killed, which is an even more annoying failure.

So the root cause is the same (a timeout), but the effect depends on
HTTP/1.1 vs HTTP/2. I was able to reproduce both cases on my local
Debian unstable system by dropping the timeout as you suggested. Running
t5551 with GIT_TEST_LONG yields a failure, whereas running t5559 yields
a hang.

We can mitigate both cases by bumping the timeout value, since it's
addressing the root cause.

There's an open question of whether this is just papering over a problem
that real users might experience, and whether Git should be doing more
to keep the connection alive. I think it's probably OK to ignore this in
practice. This is an intentionally large request being served by a very
underpowered platform. The default apache timeout is 60s. If a
real-world server is seeing ls-refs requests take that long then they
probably need to reconsider some other decisions, from ref packing to
better hardware to dropping some users. ;) I don't think trying to
insert keepalives at the Git layer here is worth the trouble.

To give a sense of the time options, here are a few timings from my
local machine, timing "git upload-pack . </dev/null >/dev/null" in
t5551's big repo.git (that's a v0 advertisement, but it should be
roughly the same work as the v2 ls-refs).

  cold-cache, refs not packed:
  real	0m9.973s
  user	0m0.354s
  sys	0m1.364s

  warm cache, refs not packed:
  real	0m0.410s
  user	0m0.153s
  sys	0m0.257s

  cold-cache, refs packed:
  real	0m0.149s
  user	0m0.086s
  sys	0m0.035s

  warm cache, refs packed:
  real	0m0.069s
  user	0m0.054s
  sys	0m0.016s

So 10s is pretty abysmal (and on an SSD, no less). I would expect the
cache to be warm (we just wrote these refs!) but I could also believe
that CI systems are under heavy I/O and memory pressure, so we sometimes
end up crossing the 60s mark.

So bumping Apache's timeout to 600s or something would probably be a
fine mitigation. That's still not _solving_ the problem, but presumably
an order of magnitude is enough for it to never come up in practice.

Michael suggested packing the refs as a mitigation. I was lukewarm on
that in my previous email, because it wasn't clear to me how close we
were on the timeout budget, and if it would just make the race less
frequent (rather than never happen). But seeing those cold-cache numbers
makes me think it might be worth doing just on principle to make the
tests more efficient, and any timeout mitigation is a bonus.

Of course the pack-refs process (and the initial ref writes) will still
have to touch all of those loose files, so those will still be slow. But
they're not on a timeout, and I suspect we read the result many more
times than we write/pack (the test failures we are seeing are not in the
expensive tests, but just "normal" tests that are stuck with the
gigantic ref state).

-Peff

Re: [RFH] Why do osx CI jobs so unreliable?

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

> If the problem is a racy deadlock, there is a reasonable chance that
> some jobs may simply be lucky. Even if things like packing refs help, I
> suspect the problem may still be lurking. Maybe I'm just a pessimist,
> though. ;)

I share the pessimism X-<.

> We had some HTTP/2 stalls/deadlocks in the past, and they were dependent
> on libcurl and apache (actually h2_mod) versions. IIRC some of the
> non-TLS code paths for HTTP/2 were not well tested, which led to
> 8f2146dbf1 (t5559: make SSL/TLS the default, 2023-02-23). Of course
> after that commit those cleartext code paths should not be a problem, so
> that is probably not exactly the issue now.
>
> But it might be worth checking the versions you're running locally
> versus what's in the GitHub runner.

True.